A titular see of Asia Minor, suffragan of Edessa. The native name of this city is not known, but it owes its Greek name to the Emperor Marcus Aurelius. Marcopolis is described at the beginning of the seventh century by the geographer George of Cyprus ("Descriptio orbis romani", ed. Gelser, 46), and in the "Notitiæ episcopatuum" of Antioch (sixth century) is alluded to as a see of Osrhoene (Echos d'Orient, X, 145). Two of its early bishops are known: Cyrus, who attended the Council of Ephesus in 431 (Mansi, "Conciliorum collectio", IV, 1269; V. 776, 797) and Caioumas, present at the Council of Chalcedon in 451 (Mansi, "Conc. coll.", VI, 572, 944; VII, 148). Eubel ("Hierarchia catholica medii ævi", Munich, I, 341) mentions four other titulars between 1340 and 1400, and a fifth from 1441 to 1453 (ibid., II, 204). The site of this city has not been found.